Rotation angle detector

ABSTRACT

A rotation angle detector provided with a spring to thrust a rotary body against protrusions formed on an inner wall of an opening via a detector body in a manner to keep the rotary body rotatable without any play in a linked motion with a steering shaft. As a result, the detector can detect rotation angles of the steering shaft with high accuracy.

FIELD OF THE INVENTION

The present invention relates to a rotation angle detector used for a steering wheel of an automobile or the like.

BACKGROUND OF THE INVENTION

FIG. 4 is an exploded perspective view of a rotation angle detector of the prior art. Rotary body 51 is disposed to case 52 in a rotatable manner with cylindrical portion 51C inserted in opening 52A. When used in an automobile, a steering shaft (not show in the figure) is inserted in center hole 51D, and rotary body 51 is then engaged with the steering shaft by means of boss 51B.

Detector body 53 is placed rotatably in case 52 in a manner to connect with rotary body 51 through engagement of gear 53A to gear 51A. Permanent magnet 54 is fixed to the center of detector body 53. Another detector body 55 is placed rotatably in case 52, and it connects detector body 53 through engagement between gears 53A and 55A. A number of cogs of gear 53A differs from that of gear 55A. Permanent magnet 56 is fixed to the center of detector body 55. Wiring board 57 is placed above detector bodies 53 and 55, and magnetic sensors 58 and 59 are mounted on wiring board 57 in respective positions confronting permanent magnets 54 and 56.

When the steering shaft rotates, rotary body 51, detector body 53 and detector body 55 also rotate in a linked motion with the steering shaft. Magnetic sensors 58 and 59 detect the rotations of permanent magnets 54 and 56 respectively, and send detecting signals to control circuit 60 provided with a microcomputer. The detecting signals of magnetic sensors 58 and 59 differ in cycle and phase from each other because the numbers of cogs are different between gears 53A and 55A.

Control circuit 60 calculates a rotation angle of rotary body 51, that is, the rotation angle of the steering shaft by executing a predetermined operation according to the two detecting signals and the numbers of cogs of the respective gears. The prior art technique discussed above is shown in Japanese Patent Unexamined Publication, No. 2005-3625.

In the conventional rotation angle detector discussed above, however, there is a problem that it is difficult to detect the rotation angle with high accuracy because rotary body 51 rotates eccentrically due to a gap between cylindrical portion 51C and opening 52A.

SUMMARY OF THE INVENTION

A rotation angle detector of the present invention comprises: a rotary body rotatable in a linked motion with a steering shaft; a case having an opening for rotatably supporting the rotary body inserted therein; a detector body rotatable in a linked motion with the rotary body; and a thrusting device for providing thrust on one of the rotary body and the detector body in a direction of the other, wherein the opening is provided with a plurality of protrusions formed on an inner wall thereof. The rotary body thrust by the thrusting device stays in pressed contact to the plurality of protrusions at all the time, and thereby becomes rotatable without any play and eccentricity. As a result, the detector can detect rotation angles with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an upper view of a rotation angle detector according to a first exemplary embodiment of the present invention;

FIG. 2 is an exploded perspective view of the same rotation angle detector;

FIG. 3 is an upper view of a rotation angle detector according to a second exemplary embodiment of the present invention; and

FIG. 4 is an exploded perspective view of a rotation angle detector of the prior art.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the accompanying drawings, description is provided hereinafter of the exemplary embodiments of the present invention.

First Exemplary Embodiment

FIG. 1 is an upper view of a rotation angle detector according to the first exemplary embodiment of this invention, and FIG. 2 is an exploded perspective view of the same. Rotary body 1 provided with gear 1A is disposed to case 12 made of a synthetic resin in a rotatable manner with cylindrical portion 1C inserted in opening 12A. Opening 12A has a dimension slightly larger than that of cylindrical portion 1C. When used in an automobile, a steering shaft (not shown) is inserted in center hole 1D, and rotary body 1 is then engaged with the steering shaft by means of boss 1B.

First detector body 3 is placed rotatably in case 12 in a manner to connect with rotary body 1 through engagement of gear 3A to gear 1A. Permanent magnet 4 is fixed to the center of first detector body 3 by insertion molding or the like method.

Second detector body 5 is placed rotatably in case 12, and it connects with first detector body 3 through engagement between gears 3A and 5A. A number of cogs of gear 3A differs from that of gear 5A. Permanent magnet 6 is fixed to the center of second detector body 5.

Wiring board 7 is placed above first and second detector bodies 3 and 5. Magnetic sensors 8 and 9 are mounted on wiring board 7 in respective positions confronting permanent magnets 4 and 6.

Permanent magnet 4 and magnetic sensor 8 constitute first detector device 13 for detecting rotation of first detector body 3, and permanent magnet 6 and magnetic sensor 9 constitute second detector device 14 for detecting rotation of second detector body 5.

Spring 15 made of steel or copper alloy serving as a thrusting device has its one end fixed to case 12, and the other end providing thrust on first detector body 3 in a direction of rotary body 1.

A plurality of protrusions 12B are formed on an inner wall of opening 12A in locations at both sides symmetrical with respect to the center line of the thrust in an area sustaining a pressure of the thrust.

Rotary body 1 thrust by first detector body 3 stays in pressed contact to the plurality of protrusions 12B.

FIG. 1 shows a structure in which rotary body 1 is retained by two protrusions 12B forming an angle of about 120 degrees with respect to the center of opening 12A. This structure is suitable since it can retain rotary body 1 in a well balanced state.

When the steering shaft rotates, rotary body 1, first detector body 3 and second detector body 5 also rotate in a linked motion with the steering shaft. Magnetic sensors 8 and 9 detect the rotations of permanent magnets 4 and 6 respectively, and send detecting signals to control circuit 10 provided with a microcomputer. The detecting signals of magnetic sensors 8 and 9 differ in cycle and phase from each other since the numbers of cogs are different between gears 3A and 5A.

Control circuit 10 calculates a rotation angle of rotary body 1, i.e., the rotation angle of the steering shaft by executing a predetermined operation according to the two detecting signals and the numbers of cogs of the respective gears, and sends the result to an electronic circuit inside a compartment of the automobile (not shown) through a signal line (not shown).

Rotary body 1 thrust by spring 15 via first detector body 3 stays in contact with the plurality of protrusions 12B at all the time, and it can thus rotate without any play and eccentricity. As a result, the detector can detect rotation angles with high accuracy.

Rotary body 1, first detector body 3 and second detector body 5 may each be provided with a material of high friction such as a rubber roller around the periphery instead of the cogs, so as to make them rotatable in the linked motion by their friction.

Second Exemplary Embodiment

FIG. 3 is an upper view of a rotation angle detector according to the second exemplary embodiment of this invention. Spring 16 serving as a thrusting device thrusts rotary body 1 in a direction of first detector body 3. A plurality of protrusions 12C are formed on an inner wall of opening 12A in locations at both sides symmetrical with respect to the center line of the thrust in an area sustaining a pressure of the thrust. Rotary body 1 thrust by spring 16 stays in pressed contact to the plurality of protrusions 12C. The structure here is identical to that of the first exemplary embodiment except that it is not provided with spring 15. Rotary body 1 thrust by spring 16 stays in contact with the plurality of protrusions 12C at all the time, and it can thus rotate without any play and eccentricity. As a result, the detector can detect rotation angles with high accuracy in the like manner as the first exemplary embodiment. 

1. A rotation angle detector comprising: a rotary body rotatable in a linked motion with a steering shaft; a case having an opening for rotatably supporting the rotary body inserted therein; a detector body rotatable in a linked motion with the rotary body; a detector device for detecting rotation of the detector body in a form of detecting signal; a control circuit for detecting a rotation angle of the rotary body from the detecting signal of the detector device; and a thrusting device for providing a thrust on one of the rotary body and the detector body in a direction of the other, wherein a plurality of protrusions are formed on an inner wall of the opening of the case and thrust by the rotary body.
 2. The rotation angle detector according to claim 1, wherein the plurality of protrusions are formed in locations at both sides symmetrical with respect to the center line of the thrust provided by the thrusting device. 